#define Magic ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define tsts int t; cin >> t; while(t--)
#include <bits/stdc++.h>
using namespace std;
using lli = long long int;
using ull = unsigned long long int;
using ld = long double;
using str = string;
#define pb push_back
#define pf push_front
#define sz size()
#define bg begin()
#define ers erase
inline void debugMode() {
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif // ONLINE_JUDGE
}
int main(){
Magic
//debugMode();
lli n, m, mn = 1e18 + 100;
cin >> n >> m;
lli a[n], b[n], s[n];
for (lli i = 0 ; i < n ; i++)
cin >> a[i];
for (lli i = 0 ; i < n ; i++)
cin >> b[i];
for (lli i = 0 ; i < n ; i++){
s[i] = max(a[i], b[i]) * m;
mn = min(mn, s[i]);
}
lli l = mn, r = 1e18;
//r = 19;
//l = 17;
while (r - l > 1){
lli mid = (r + l)/2, k = 0;
//cout << mid << "\n";
for (lli i = 0 ; i < n ; i++){
if (s[i] > mid){
k+=(s[i] - mid)/max(a[i], b[i]);
}
if (s[i] < mid){
k-=((mid - s[i])/b[i]) + (((mid - s[i]) % b[i]) > 0);
}
}
if (k >= 0)
l = mid;
else
r = mid;
}
cout << l;
}
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣠⠤⢲⣦⡀⠀⣠⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣀⣀⣀⣠⠖⠚⠓⠒⠒⠲⠿⣍⣛⣻⣦⣷⢠⣻⣀⠤⠤⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣠⠔⡿⠓⠲⠬⢥⡤⠤⠤⠤⠤⣤⣀⣀⣈⣻⣿⣿⠓⠉⣀⡤⠔⢶⣻⡆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣤⢤⠞⠁⣼⠀⠀⠀⠀⠀⠀⠰⠶⢌⣽⡶⠟⢏⡁⢈⣉⣭⣷⡯⣝⠒⢦⣄⠙⠷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⡾⣵⠿⣳⡟⠉⠉⠿⠀⠀⡀⠀⠀⣀⣀⣢⣾⣿⡚⠓⠒⠒⠒⠻⢿⣟⣧⡀⢠⣢⡻⠙⣄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⡀⢿⣟⣲⢿⣷⢀⣤⣠⣄⣈⢿⣷⣤⣷⣻⡓⠒⠻⠭⢷⡄⠒⠲⢶⣦⣬⣻⣏⢦⡈⢿⣆⠘⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢠⢖⣩⠷⢎⣙⣿⣿⣼⡼⣿⣟⣽⣻⢯⢿⠞⣌⠙⢳⡕⠀⠙⠲⣶⠤⢄⡠⣄⡈⠛⣿⣿⣧⢳⣌⢻⡆⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠰⠗⠉⢀⣾⠟⠒⡿⣫⡿⡾⢫⢟⡏⠉⢸⡀⠑⢾⡆⢤⣻⣶⣤⣘⣲⣿⣶⡽⠿⣯⠲⣌⣇⢹⣷⣿⣆⠸⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠀⠀⡼⠀⣿⢣⣧⠋⣸⠀⣰⢀⣿⣆⠀⠰⣄⠙⣧⣨⣿⣿⣿⣯⣿⣦⠘⣷⡌⢻⡄⠿⣆⠟⣆⢇⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⠀⠀⠀⠀⠀⠀⠀⠀⡇⡼⣹⠈⢣⠆⡇⣰⣻⣼⣿⣽⣷⣦⣹⣿⣟⣯⠉⠘⣿⠏⠃⠀⣷⣽⡿⣾⡹⣷⣹⣧⡈⢺⡀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣠⢾⠟⠉⠀⠀⠀⠀⠀⠀⠀⠀⣷⣱⣽⡀⢸⣆⢳⣿⣇⣷⡿⠖⠿⠷⢦⣙⣆⠩⡗⠀⠀⠀⠀⠀⡯⠿⠳⣟⠻⣽⣄⢧⠈⠳⣷⡀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⣸⡇⡏⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣤⣿⣿⣷⣸⣿⡀⣿⣅⠛⠇⠀⠀⠀⠀⢈⠙⠂⠀⠀⠀⠀⠀⣸⣿⠀⢠⣜⢦⠘⢿⣮⣷⡀⠀⠙⢦⡀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⢯⣇⠙⢄⣀⠀⠀⠀⢀⣀⡠⣴⣾⣫⠵⠛⣿⣻⠿⣷⣹⣾⣷⡠⡀⠀⠀⠀⠻⠦⠀⣀⠔⠀⠀⣴⣿⣸⣧⡀⠳⣝⠳⢴⡙⢞⣏⠢⡀⠀⠹⡄⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⢀⣀⣀⣈⣻⣤⣀⠈⠉⠻⠿⢿⣺⣿⡵⣶⢶⣦⠀⠘⣿⢷⣾⢿⣿⡋⢙⣮⣄⡀⠀⠀⠉⠈⠀⠀⢀⢞⣿⣼⣿⣿⣿⣆⡀⠙⢦⣝⣮⠛⢷⡙⢆⠀⣷⠀⠀⠀⠀
///⠀⠀⠀⢠⡴⢟⣫⠤⠖⠒⠛⢛⣲⣿⣿⣿⠟⠋⢱⣿⣴⣷⣿⣹⢃⣀⣘⠃⢩⢿⣫⣥⣿⠧⢿⣿⣗⡶⣤⣄⣀⣴⣷⣻⣿⣿⠻⠘⣏⠛⢿⣦⣀⠱⢤⣉⡑⠛⠮⢿⣹⠀⠀⠀⠀
///⠀⢠⢖⠵⠊⠁⢀⡤⠖⣲⣿⣿⣟⣻⣿⣋⠀⠀⠈⢿⣿⡿⠟⣵⣿⣿⣿⣷⡏⠈⢿⡿⣷⣤⣼⢿⣿⣿⢶⣯⣭⣵⣾⢿⣿⠿⢦⡀⢹⠀⠈⣏⠉⠉⢻⣶⣯⡑⠦⣄⠈⠳⣄⠀
///⠀⠹⠁⠀⠀⣞⢁⡾⢽⣯⣝⣛⣛⣯⣭⣽⣿⣷⣶⣤⣤⣴⣿⣿⣿⣿⣿⣿⡀⣀⣼⣀⠈⠙⠛⠷⣾⡿⢿⡟⣿⠟⠁⣈⣥⡴⠾⠷⢾⡄⠀⣿⠀⠀⠈⢇⠘⣿⣤⣀⠑⢦⡘⢧⠀
///⠄⠀⠀⠀⠀⠈⠻⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⢿⡿⠛⣻⢏⡽⣯⡄⠘⣏⣿⡏⠈⠙⠓⠶⣤⣀⠀⠙⢿⣿⡇⢀⡿⠋⠁⠀⢀⣀⣸⡇⠀⣟⣀⠀⠀⠀⠙⠃⣿⡎⠑⣤⡙⣌⡇
///⠀⠀⠀⠀⠀⠀⠀⠙⢿⣿⣿⣿⣿⣿⣿⣿⡥⣖⡯⠖⢋⣡⡞⣼⣿⠀⠀⢹⣿⣷⠀⠀⣀⡀⠀⠉⠻⣦⠀⢿⣿⡿⠁⣠⡶⠟⠋⠉⠹⣆⣸⣿⣿⠀⣀⡤⣤⡀⣿⠇⠀⢸⠳⡜⡇
///⠀⠀⠀⠀⠀⠀⠀⠀⣈⣿⣿⣿⣿⣿⣿⣏⢿⣗⠒⠊⠉⢸⠁⡿⡏⠀⢀⣿⡿⣁⠤⢶⣿⣽⡆⠀⠀⠘⢷⡈⠉⣡⠾⠋⠀⠀⣠⣆⢠⣿⣿⣿⡟⢀⣷⠒⢺⣧⡏⠀⠀⢸⠀⢹⣹
///⠀⠀⠀⠀⠀⠀⡠⢪⠟⡽⠙⢶⣾⣿⣿⣿⣷⡻⣦⡀⠀⠀⢣⣇⡇⢀⡞⣸⠏⠁⠀⠀⡇⢻⡀⠀⠀⣾⣶⡟⣿⣥⡄⠀⠀⢠⣇⣼⡶⣿⣿⠋⣸⣾⣷⣚⣽⡟⠀⠀⠀⣏⠀⡼⣿
///⠀⠀⠀⠀⢀⠎⡴⣣⣾⠟⣡⠞⢹⡿⣿⢿⣿⣿⣿⣷⣄⠀⠈⠻⡹⣼⠀⣿⡄⠀⠀⠀⠉⠻⣷⡀⠀⠙⠿⠇⣿⠿⠇⠀⠀⢠⡿⠋⢇⢹⣟⢷⠫⣿⣟⡿⠋⠀⠀⣠⣾⢞⡜⠁⡿
///⠀⠀⠀⠀⡼⡼⣵⠏⡏⣰⠃⠀⢾⡇⠈⠻⣿⣮⡉⠹⣿⣧⣄⡀⠙⣇⠀⠸⣿⣄⡀⠀⠀⠀⠈⢉⣧⡴⠀⠠⡄⣀⡤⠤⠴⠋⠁⠀⠈⢻⣿⣾⣤⡿⠋⠀⠀⠀⣉⣽⠿⠋⠀⣰⠃
///⠀⠀⠀⠀⣿⣽⠋⠀⡇⡇⠀⠀⠘⣷⢠⣶⢮⣻⣿⣦⠈⠛⠙⠹⣷⠘⢦⣤⣿⣳⣭⣑⣒⣒⣺⣿⢿⣀⣀⣀⣿⣧⣀⣀⣀⡤⠴⠒⣶⣿⣏⣾⡿⠁⠀⠀⠀⠉⠉⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⢻⡏⠀⠀⢳⣇⠀⠀⠀⠈⠈⣿⣾⣿⣿⣮⣿⣦⠀⠀⢿⣶⡫⣿⣿⣿⣿⣿⡹⣯⣊⠁⠉⠉⠉⠉⢙⣮⣷⣶⡤⣤⣶⣿⣿⣟⣾⢿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠸⣿⣦⡀⠀⠙⠦⠀⠀⢀⣼⠿⣽⣿⣯⣷⣼⡷⢾⣻⣾⣿⠞⢿⢻⡷⠻⣿⣏⡙⢝⣻⡾⡖⠒⣻⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡟⣎⠣⣀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠈⠁⠀⠀⠀⠀⣴⣋⣉⣩⣿⣿⢿⣟⣷⣾⣯⡟⢱⡇⠀⠘⣿⠣⡀⣈⣻⣿⣿⣿⣷⣷⣶⣿⣿⣟⠋⡿⣹⣿⣿⣿⣿⢟⣏⠺⠿⠶⠭⠷⠂⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⢰⣿⣿⣿⣿⣿⣿⣿⢹⣮⣾⣿⡿⢋⣶⢸⡇⠀⠀⠈⢷⡑⠈⢻⣟⠛⠛⠿⠋⠙⠓⣭⣿⣹⣵⣿⣿⣿⣿⣿⠈⠻⣷⣄⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠙⢟⣛⡭⠶⢾⡿⠃⠀⠀⢸⢹⣾⣇⠀⠀⠀⠀⠻⣟⣿⡏⠀⠀⠀⠀⢰⣿⣿⢿⡇⣿⣿⣿⣿⣟⡏⠀⠀⠀⠉⠙⠓⠒⠂⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢠⡟⠀⠀⠀⢰⣿⢸⣿⢿⡀⠀⠀⠀⠀⢸⣿⣣⠀⠀⠀⢠⣿⡟⣷⣾⣿⢿⣿⣿⣿⣿⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣿⠁⠀⠀⠀⠘⡿⡿⢿⣏⣧⠀⠀⠀⢀⣾⣿⠿⠀⢀⣴⣿⣿⢿⡹⡇⣿⠈⣿⣿⡟⣾⠇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⣿⡇⠀⠀⠀⠀⢳⢧⠈⢿⣿⠀⠀⢀⣼⣿⠕⠁⣠⣾⡿⣻⠏⠀⢹⣹⣿⣆⣿⣿⣿⣿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣾⣿⣷⠀⠀⠀⠀⠈⣏⢧⠀⢻⣧⠶⣋⠿⠋⣀⣾⣟⣿⠞⠁⠀⠀⠀⢯⣿⣿⣿⣿⣿⡏⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢻⣿⣿⣇⠀⠀⠀⠀⠸⡜⣆⠈⢷⣿⠀⢠⣾⣿⠟⢻⡏⠀⠀⠀⠀⠀⠘⣿⣿⠏⣿⣿⠃⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⡻⣿⣿⣦⡀⠀⠀⠀⢧⠘⣆⠈⢷⠒⠛⢻⡿⠄⠘⣧⠀⠀⠀⠀⠀⢰⣷⣹⠀⠙⣿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⣷⣝⣿⣿⣷⣄⠀⠀⠈⢇⠸⡄⠈⣇⠀⠀⢻⣆⠀⠘⣇⠀⠀⣠⣾⣽⢹⡟⠀⢰⣷⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢻⣾⢻⠙⢿⣿⡇⠀⠀⠈⢧⢳⠀⢸⡀⠀⠀⢻⣆⠀⢻⡄⢠⣿⣯⣽⣓⣧⣤⠾⢹⣿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⣿⣼⡇⠀⠙⣿⠀⠀⠀⠈⢏⢧⠀⣇⠀⠀⠀⢻⣆⠀⢷⠘⣿⣮⡻⣿⠁⠀⢀⣯⣿⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢿⣿⣧⡀⠀⠀⠀⠀⠀⠀⠘⡾⡄⢸⠀⠀⠀⠈⢻⣆⠈⢷⣷⣾⣟⣻⣶⣿⡿⠛⢿⣷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⣿⣿⣿⣦⣀⠀⠀⠀⠀⠀⢳⣇⠘⡆⠀⠀⠀⠀⠻⣶⢺⡏⢹⡟⠀⠉⠁⠀⠀⠀⢩⣍⠙⡆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠸⣟⣿⣿⣿⣧⠀⢀⣤⣤⡸⣸⠀⡇⠀⠀⠀⠀⠀⠙⣿⣷⢡⣿⣶⣄⠀⠀⣄⠀⣦⣍⠙⢳⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠹⡿⢿⡙⠿⠀⢸⡟⢲⣷⡿⡄⢿⠀⠀⠀⠀⠀⠀⠘⣏⢸⣇⣍⢻⣷⣀⢻⣦⣤⣌⡙⣦⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠹⣯⢷⠀⠀⠸⡇⠀⢿⣧⡇⢸⠀⠀⠀⠀⠀⠀⠀⣼⢸⣿⣯⠀⣿⣿⣷⣝⣿⣻⣿⣼⣷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢻⣎⣧⠀⠐⣇⠀⠘⣽⣿⡸⡆⠀⠀⠀⠀⠀⠀⠈⠋⠈⠻⣼⣿⢶⢿⣿⣯⡻⣿⣿⣾⣷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢻⡼⡆⠀⣿⡀⠀⣿⢿⡇⢷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⣿⣾⢧⠈⠙⠿⣮⠟⠉⠙⢦⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⢿⢻⢠⣿⡇⠀⠹⣄⢳⣜⡆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢹⡏⠪⠳⢤⣄⣀⠀⠀⠀⠈⢣⠀⠀⠀⠀⠀⠀⠀⠀⠀
///⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⣎⣿⡟⡇⠀⠀⠈⢻⣿⣷⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢳⡄⠀⠀⠀⠙⢧⡀⢀⡄⠈⡇⠀⠀⠀⠀⠀⠀⠀⠀
